Multiple fuel carburetor

ABSTRACT

A carburetor with two fuel bowls and floats has a double-ended needle valve operative between the exit ports of both bowls directly between the bowls and the venturi jet of the carburetor such that the different grade fuels in the two fuel bowls are alternately supplied to the venturi jet and thence to the motor under the control of a valve actuator. The valve actuator is responsive to the engine manifold vacuum level such that high grade fuel is dispensed to the carburetor under low manifold vacuum conditions and low grade fuel is dispensed to the carburetor under high manifold vacuum conditions. Various fuel bypass and vacuum bypass lines are provided in the carburetor and to a dashboard control panel such that the engine may operate exclusively on either fuel.

United States Patent [1 1 Madariaga [4M Apr. 23, 1974 Primary Examiner-Wendell E. Burns Attorney, Agent, or Firm-Wm. .lacquet Gribble [57] ABSTRACT A carburetor with two fuel bowls and floats has a double-ended needle valve operative between the exit ports of both bowls directly between the bowls and the venturi jet of the carburetor such that the different grade fuels in the two fuel bowls are alternately supplied to the venturi jet and thence to the motor under the control of a valve actuator. The valve actuator is responsive to the engine manifold vacuum level such that high grade fuel is dispensed to the carburetor under low manifold vacuum conditions and low grade fuel is dispensed to the carburetor under high manifold vacuum conditions. Various fuel bypass and vacuum bypass lines are provided in the carburetor and to a dashboard control panel such that the engine may operate exclusively on either fuel.

2 Claims, 8 Drawing Figures H/GH LOW 0cm NE OCT NE SUPPL l SUPPL l J a 96 9 a4 46 PATENTEnAPm I914 3805756 INVENTOR. FLAVIO MADARIAGA T TORME Y MULTIPLE FUEL CARBURETOR BACKGROUND OF THE INVENTION A Dual fuel systems for engines have long been suggested to accomplish economies in engine performance. Most dual fuel systems previously disclosed have relied upon blending fuels in response to manifold pressure conditions. The relationship between manifold vacuum condition and the need for high grade or low grade fuel is ably set forth in the US. Letters Patent to Boller (2,652,237) entitled Two Fuel Carburetor issued Sept. 13, 1953. As explained in that patent, low vacuum manifold conditions indicate high power requirements that demand a more powerful fuel, such as high octane leaded gasoline, while high vacuum manifold conditions indicate lower power demands that may be satisfied by low grade fuels, such as lower octane unleaded gases, diesel or distillate fuels.

The ecological deterioration in the United States and other countries, particularly in highly urbanized areas, has led to intensive investigation of means to reduce the contaminants in the air stemming from combustion of petroleum products. Internal combustion engines require high compression ratios for efficiency. High compression engines, however, will not normally operate on a lowgrade or low octane fuel because of preignition" or knocking." Therefore, tetra-ethyl lead is added to gasoline to raise the octane rating to make it suitable for high compression engines. Tetra-ethyl lead, however, has been proven to be a hazardous and dangerous ecological pollutant and also interferes with the operation of antipollution catalytic automobile mufflers. The automotive industryhas responded to demands for a cessation of leaded gasoline consumption by reducing the compression ratio and retarding the spark of the 1971 automobile engines. While this procedure permits the engines to operate on lower octane fuel, it reduces engine efficiency and thus increases over-all fuel consumption. Therefore, the steps taken to eliminate lead pollution have increased the over-all combustion of petroleum products, further increasing the ecological deterioration by the increased discharge of unburned and burned hydrocarbons due to the poor fuel economy.

While the petroleum industry can produce only limited quantities of high octane unleaded fuel, it can produce unleaded low octane fuels in quantities sufficient to meet any foreseeable demand. Tests have shown that the dual fuel carburetor uses about four parts of low grade to one part highgrade fuel; thus the demand for high grade fuel could be reduced to thepetroleum industrys capacity to produce high octane unleaded fuel, or in any event, the amount of highly leaded fuel needed for the existing high compression engines could be drastically reduced. It is therefore an objective of the present invention to provide a carburetor adapted to a dual fuel system which provides the required fuel to the engine in response to manifold vacuum conditions without impairing the efficiency of the engine.

SUMMARY OF THE INVENTION The invention contemplates, in an internal combustion engine for use with two fuel supplies and having a fuel intake or carburetor with a throttle valve therein, the combination which comprises first and second fuel bowls or float chambers connected, respectively, to

first and second fuel supplies, with afuel passage to the fuel intake means from the fuel bowls. A double-acting valve intervenes between the fuel bowls and the fuel passage. Actuator means responsive to engine manifold vacuum conditions displaces the valving member between mutually exclusive open positions with respect to each fuel bowl. Further means meters the fuel flow between the valving member and the fuel passage.

In one embodiment interrupter valves intervene between the actuator means and the engine manifold such that the vehicle operator may select which of the two fuels is used for starting and idling.

An object of the invention is to provide a multiple fuel carburetor wherein one of two fuels flows to the carburetor in response to the power requirements of the engine.

A further object of the invention is to provide such a carburetor wherein the vehicle operator may select which of the two fuels is used to supply the idling engine and for starting the engine.

Another object of the invention is to provide valving means responsive to engine vacuum manifold conditions wherein either high or low octane fuel is exclusively provided to the intake means at one time.

A further object of the invention is to provide a carburetor wherein a wide range of fuels may be utilized as the high octane and low octane fuels.

The carburetor of the invention thus provides economical engine performance under all operating conditions while minimizing the use of high tetraethyl lead gasoline with its deleterious effect upon the atmosphere with no sacrifice of engine: performance.

These and other advantages of the invention are apparent in the following detailed description and draw mg.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a schematic sectional elevation of a multiple fuel carburetor in accordance with the invention having operator control means;

FIG. 2 is an enlarged fragmentary sectional elevation of the valving member of the embodiment of FIG. 1;

FIG. 3 is a plan view of the embodiment of FIG. 1 to a reduced scale;

FIG. 4 is a schematic fragmentary sectional elevation of an alternate embodiment of the invention having a three-stage valving member;

FIG. 5 is an enlarged fragmentary sectional elevation of the three-stage valving member of the embodiment of FIG. 4;

FIG. 6 is a schematic sectional elevation, partly broken away, of a further alternate embodiment of the invention with no operator controls;

FIG. 7 isa fragmentary plan section taken along line 7-7 of FIG. 6; and

FIG. 8 is a fragmentary schematic sectional elevation, partly broken away, of a further alternate embodiment of the invention.

In the various Figures like reference characters are used to designate like parts.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIGS. 1, 2 and 3 illustrate schematically a multiplefuel carburetor 10 connected to a control console 11 which is shown by phantom lines. Preferably the carburetor comprises an upper body casting 12 and a lower body casting 13 joined alonga parting line 14 by a plurality of screws, such as the hex-head screw 15, and the slotted screws 16. If necessary, a gasket (not shown) may be used for sealing between the two body castings.

Upper casting 12 has a cylindrical wall 17 which defines a carburetor intake throat 18 in which a choke butterfly valve 19 is pivotally mounted to be manipulated in conventional fashion between the open position of the solid lines and the closed position shown by the dotted lines 21. A suitable air filter (not shown) may be mounted to the wall 17, as desired.

An actuating control housing 23 extends from the cylindrical wall and contains an actuating cylinder 24 in which a piston 25 may reciprocate. The upper casting continues from the housing 23 in a float bowl cover 28 which seals the upper openings of a pair of float bowls 31, 32 in which conventional valve floats represented by circles 34, 35, respectively, are operable. In conventional fashion the valve floats operate valves intervening between the bowls 31, 32 and conventional fuel pumps 37, 38, respectively, which deliver fuel to the float bowls from a low octane supply tank 41 and a high octane supply tank 42. Low octane tank 41 is connected through pump 37 to bowl 31 while high octane tank 42 is connected through pump 38 to bowl 32.

Lower casting 13 has formed therein in axial alignment with intake throat 18 a restricted venturi throat 44 which expands downwardly into a throttle chamber 45 in which a throttle valve 46 is movable between the solid line open positions and the closed, or idle, position represented by dotted lines 48.

Beneath control housing 23 the lower casting 13 extends in a thick web 51 which connects to a wall 52 of float bowl 32. Wall 52 is parallel to a wall 53 which divides float bowls 31, 32. The float bowls are further defined by end walls such as the walls 54, 55 and by a floor 56 which extends beneath both bowls. A conduit rib 57 protrudes exteriorly from floor 56 and contains a drilled or cored conduit 59 which connects to a threaded bore 61 ofa bowl boss 62 which projects into float bowl 32. Threaded bore 61 is sealed at its bottom by a manifold screw 64 which has a central valve port 65 connected to an exterior groove 66 by a plurality of radial holes 67. Conduit 59 connects with groove 66 for flow into central port 65.

An externally threaded valve body 71 seals the upper portion of threaded bore 61 and is chambered to define a valve port for a compound valving member 72. The specific configuration and operation of the valving member is set forth later on with respect to FIG. 2.

The respective ends 74, 75 of the manifold screw 64 and valve body 71 are separated within bore 61 by an annulus 76 which connects to a drilled or cored fuel chamber 77 which angles downwardly to be intercepted by a conventional threaded metering jet bore 79 in which a threaded jet 80 lodges to retain a venturi tube 81 which terminates centrally of the venturi throat 44 in conventional fashion. The metering jet bore intercepts a vertical passage 82 connecting with chamber 77. The tube end has an axial metering passage 83. The simple substitution of the jets 80 with varying metering passages 83 provides for wide range adjustment of the air-fuel mixture provided to the carburetor intake from the fuel chamber 77. Plug 84 closes bore 79.

A conventional spring-biased idling valve 85 with a conventional air bleed is adjustable within a boss 86 on the lower casting within an idle passage 87 which enters the throttle chamber 45 between the intake manifold and the closed or idle position of throttle valve 46. Fuel is supplied to the idling passage through drilled or cored passageways 88, 88A which connect to the fuel chamber 77 through a conventional idler tube 89 in passage 90.

Opposite the idling valve the lower casting has an exterior boss 91 in which tubing connectors 92, 93 are threadably engaged. From each connector a passage extends into the throttle chamber 45 of the carburetor. From connector 92 a passage 95 extends to a point between the closed position of the throttle and the engine intake manifold (not shown). A passage 96 extends from connector 93 to a point between the venturi tube 81 and the closed position of the throttle valve.

In some instances it may be desirable to manually control which fuel is used under certain operating conditions. A first elongate tube 97 therefore extends from connector 92 to the control console 11 within the operators cab in the vehicle. A valve 98 in the tube, schematically represented, intervenes between the passage 95 and a continuing tube portion 99 which extends to a threaded tube connector 101 connecting the elongate tube to the chamber 24 of the valve control. A second elongate tube 104 extends from passage 96 and connector 93 to tube portion 99. A second valve 105 intervenes in the tube 104 between the passage 96 and tube 99 extending to the valve control. Each of the valves may be turned by means of its control 106 to close the lines 97 and 104, respectively.

Piston 25 reciprocates in cylinder 24. The piston has an elongate shaft 112 which terminates within float bowl 32 in a flange 113. A threaded plug 115 closes the bottom portion of cylinder 24 and stem 112 slides therein in a central port 116 which may be suitably sealed against the stem as by O-rings (not shown). A compression spring 118 biases the stem and piston 25 downwardly in FIG. 1 toward valving member 72. The downward force of the spring is counterbalanced or overcome by the partial vacuum created in either passage 95 or passage 96 by the vacuum condition of the intake manifold of the engine, communicated to cylinder 24 through either line 97 or line 104 and tube portion 99.

As can be seen from FIG. 2, valving member 72 comprises a needle 121 which terminates at one end in a first conical valve 122 and at its other end in a second conical valve 123. Valve 122 is adapted to seat within a valve port 125 of the valve body 71. Conical valve 123 seats within the central valve port 65 of manifolding screw 64. The inner cavity valve body 71 is.partially closed by a concave retainer 127 which has a plurality of apertures 128 through which fuel flows from high octane float bowl 32 through port 125 and out of the valve body 71 into fuel chamber 77. The retainer also holds a compression spring 129 between the bottom shoulder 131 of first valve 122 and the retainer. Valving member 72 is thus biased to close port 125 by the spring 129.

It is thus evident that fuel may flow from either float bowl 31 with its low octane supply or float bowl 32 with a high octane fuel into fuel chamber 77 and thence through metering jet 83 and the venturi tube 81 into the throttle chamber 45 of the carburetor. As shown in FIGS. 1 and 2, port 125 is closed, precluding fuel flow from high octane bowl 32. Therefore, the carburetor is being supplied from low octane bowl 31 through meter ing plug 133 and conduit 59, indicating a cruising condition of the engine. As has been stated, under cruising conditions the intake manifold has a high vacuum level and piston 25 is lifted against the bias of spring 118 such that the valve spring 129 may retain port 65 in open condition. A cylinder bleeder 134 in the housing 23 prevents air lock of the piston. When a load is imposed upon the motor, such as during acceleration or hill climbing, the intake manifold vacuum level de creases, decreasing the lift effect on piston 25 within cylinder 24 and spring 118 overcomes the weakened vacuum lift effect and makes contact with the extension 135 of valve 122, depressing valving member 72 such that port 125 is opened and the central port 65 is closed. With the central port closed, no fuel flow takes place from bowl 31 through conduit 59, but fuel flow is from bowl 32 through port 125 into fuel chamber 77 and thence through the metering jet and the venturi tube into the carburetor intake throat.

When the engine is idling, as when throttle valve 46 assumes the closed position 46, and with valve 105 open, the high vacuum level of the intake manifold is not communicated to the piston. Spring 118 biases stem 112 into contact with valve member 72 such that port 125 is opened and the engine idles on high octane fuel. With reversal of the valve positions of FIG. 1 (opening valve 98 and closing valve 105), passage 95 is in communication with the control cylinder 24 and the high vacuum condition of the intake manifold results in an upward displacement of piston 25 to release valving member 72 to close port 125 and open the port 65 permitting flow from the low octane fuel supply in float bowl 31. The car engine thereupon is idling on low octane fuel. The vacuum condition communication between the intake manifold and the cylinder 24 can in like manner be controlled to determine from the control console 11 the type of fuel which is used in starting, as by closing both valves.

The simultaneous opening or closing of the central port 65 and the port 125 is as rapid as the vacuum level change at the intake manifold. Therefore, there is little or no blending of high and low octane fuels in fuel chamber 77. Since the respective ports 65 and 125 alternate conditions almost simultaneously the optimum fuel is thereby supplied to the carburetor intake as rapidly as the intake conditions change.

In the absence of a restricting jet at 83 of the threaded metering jet, the fuel-to-air ratio in the carburetor of FIG. 1 may be determined by the area between the valve cone 122 and the port 125 when that valve is depressed. Fuel chamber 77 is sized to be nonmetering, as is the transverse passage 82. The carburetor is thus able to deliver optimum fuel-air mix for power when utilizing the high octane supply.

The low octane supply, used for low power demands, may be metered at its exit from float bowl 31 by metering jet 133 which is interchangeable such that the central metering restriction may be altered. Alternatively, manifold screw 64 may be changed.

In the embodiment of FIGS. 4 and 5 it is assumed that the low octane supply is a fuel such as kerosene and the high octane supply is a gasoline, leaded or unleaded. The carburetor 140 is in most respects similar to the carburetor 10 of the previously described embodiment, having upper and lower body castings 12 and 13 which combine to provide axially aligned carburetor intake throat 18, venturi section 44 and mixing or throttle chamber 45. The carburetor also has the previously described twin float bowls 31, 32 and actuating piston 25 within control cylinder 24. The choke butterfly valve 19 and the throttle butterfly valve 46 are conventional.

For economy during operation under cruising conditions a threaded metering jet 142 has a metering passage 143 considerably restricted when compared to jet passage 83 of the previously described embodiment. The metering jet 133A in low octane float bowl 31 has a nonmetering central jet passage 144. An annulus 76 between valve body 71 and manifolding screw 74 is connected to a metering jet transverse passage 147 by a fuel chamber 149 having a downward leg 151.

As can be seen from FIG. 5, the externally threaded valve body 71 has an exit annulus 153 connected to the cavity 126 by a plurality of radial ports 154. The annulus communicates with a bypass channel 157 which ex tends into the venturi tube 81. The channel 157 has two functions. Preferably the engine is adjusted for optimum power output on the higher octane fuel, both as to spark and air-fuel ratio. The channel therefore compensates for the lean low octane fuel mixture imposed by metering jet 143 by supplying additional high octane fuel from the valve body 71 when valve member 172 opens a valve body port 158.

In a manner to be described later, channel 157 also delivers high octane fuel to the carburetor when starting the engine, since a fuel such as kerosene is not adapted to starting a high compression engine.

Because of the functions of bypass channel 157, a compound valving system is utilized in valve body 71 to preclude passage of low octane fuel through the channel 157. As can be seen from FIG. 5, the valve member 172 has three valving portions: lower valve cone 161 to open and close central port 65 to control low octane fuel, upper valve cone 162 to shut off high octane fuel and intermediate valve cone 163 to close the valve body cavity 126 against flow of low octane fuel except into fuel chamber 149.

Valve cones 162 and 163 are so adjusted that closure of port 158 and the port 164 defined by the concave retainer 127 is simultaneous. As in the previously described embodiment, the high octane ports 158 and 164 are closed when the low octane port 65 is open and vice versa.

Varying conditions may dictate different choices as to which of the two fuels is desired. for engine idle. The embodiment of FIG. 4 is therefore provided with a series of idle passages to allow the use of either fuel for idling. Carburetor 140 has a conventional spring biased idle valve 85 having an idle passage 87 shown emerging at 87A into the throttle chamber of the carburetor. The boss 86A into which the idling valve is threaded is arcuately displaced with respect to the venturi tube such that vertical passages 165 and 166 may extend from horizontal passages 167 and 168 to establish a fuel line flow line from fuel chamber 149 to the idling valve. A conventional idler tube 169 extends into passage 165 from a threaded bore 171 which extends downwardly in thickened wall 51 from parting line 14 of the upper and lower body castings.

The various passages and channels may be established within the wall in conventional fashion by drilling, coring or other similar methods.

As in the previous embodiments, tubes 97 and 104 extend to an operators control console 11 from passages 95 and 96 which open into the throttle chamber on downstream and upstream locations, respectively,

with respect to the closed or idling position of the throttle valve 46. Valves 98 and 105 control flow through the tubes to a tube portion 99 connecting through a threaded connector 101 to a control cylinder 24 of an actuating piston 25 for valve member 72. With either valve 98 or 105 open during normal operating speeds, piston 25 is in direct communication with the condition of the intake manifold of the engine. During cruising operation, the relatively high vacuum condition of the intake manifold is communicated to cylinder 24, raising piston 25 to the position shown in FIG. 4 wherein stem 112 is separated from valving member 172 such that spring 129 of the valving member closes port 158 and opens port 65. The low octane fuel flows freely through jet 133A, conduit 59 and through manifolding screw 64 into fuel chamber 149 for delivery to metering jet 142 and the venturi tube 81. The engine thus cruises on the low octane supply. Should power demands be imposed as by climbing a hill or acceleration, the intake manifold vacuum level drops and spring 118 overcomes the lift effect on piston 25, causing stem 112 to depress valving member 72 such that port 158 and the retainer port 164 are opened and port 65 is closed. The response is instantaneous such that the high octane fuel is immediately supplied to the venturi throat from high octane chamber bowl 32. The instantaneous response is due, not only to the sensitivity of the actuating piston 25, but also due to the location proximate the venturi tube of the valving member which controls the fuel selection. No time lag therefore delays responseof the proper fuel supply to the engine need.

With the throttle valve in the closed off position 48, the operator may manipulate valves 98 and 105 to determine which fuel the engine idles on. With valve 98 open and valve 105 closed, the cylinder 24 is in communication with the manifold and the relatively high vacuum level lifts piston 25, closing the high octane chamber and opening the low octane supply such that the idling tube 169 educes low octane fuel from fuel chamber 149 and supplies such fuel through idling valve to the intake manifold.

Oppositely, when valve 98 is closed and valve 105 is opened, the control cylinder is connected with passage 96 on the upstream side of the closed throttle valve blocked from the manifold vacuum effect. The pressure at passage 96 is approximately atmospheric and piston 25 is depressed by spring 118 opening the port 158 and supplying high octane fuel into the annulus 76 and fuel chamber 149, from which fuel is educed to the idle valve 85 and into the intake manifold. Fuel jet 142 and bypass 157 educe no fuel from chamber 149 because the throttle blocks them from the draw of the intake manifold.

While separate valves have been shown for the sake of simplicity in understanding the operation of the invention shown in the embodiments of FIG. 1 and FIG. 4, the invention does not preclude a single valve connected to both line 97 and line 104 to simplify control operation.

It may be desirable in some instances, particularly where it is inconvenient or expensive to run vacuum lines from the carburetor to the control console, to provide a carburetor which is fully automatic. Such a carburetor 180 is shown in the embodiments of FIGS. 6 and 7 which, in most respects, is similar to the embodiment of FIG. 4, having a three-element valving member 172 which is impinged upon by a stem 112 biased by a spring 118. The position of the stem 112 changes in response to the action of a piston 25 within a cylinder 24 both housed in an upper body casting 12. The fuel float chambers 31, 32 of the embodiment of FIG. 6 are supplied low octane and high octane, respectively, from a low octane supply 41 and a high octane supply 42 under the influence of fuel pumps 37, 38, respectively.

Unlike the embodiment of FIG. 4, the embodiment of FIG. 6 has no elongate tubes connecting between opposite sides of the throttle valve and the cylinder 24. Instead an inner conduit 181 extends between the top of cylinder 24 and a port 182 opening into throttle chamber 45 at a point between the intake manifold (not shown) and the closed position of the throttle valve 46. Conduit 181 is comprised of a horizontal run 184 and a vertical run 185 in upper casting 12 and a vertical channel 186 between the port 182 and an angled passage 187 connecting between the channel 186 and vertical run 185. The various segments of passageway 181 establish a fluid communication conduit between the cylinder 24 and the throttle chamber 45.

A conventional idler tube 169 connects to the conventional idle valve and its passage 87 through a substantially vertical passageway 191 (shown in dotted lines) to provide for fuel from chamber 149 when the engine is idling withthe throttle valve closed.

In operation the carburetor of FIGS. 6 and 7 is similar to the operation of the previously described embodiments. Fuel is drawn from either chamber 31 or 32 of the carburetor, depending upon the position of compound valving member 172. Like the embodiment of FIG. 4, the embodiment of FIG. 6 has a high power jet 157 communicating directly with a venturi tube 81. Basic fuel flow, however, is through a fuel chamber 149 and ajet 142 to the venturi tube. As shown in FIG. 6, when throttle valve 46 is closed and the engine is idling the manifold vacuum level becomes high. The vacuum level is sensed by piston 25 through conduit 181 and the piston rises in cylinder 24. Stem 112 is drawn away from the extension of the valving member, opening port 65 such that low octane fuel flows to chamber 149. Since the closed throttle valve precludes manifold draw on the venturi tube, fuel is alternatively drawn through idle tube 169 and thence through the idle passage 191 to be introduced at the idle valve into the throttle valve chamber 45 and thence to the engine.

Should the low octane supply be a fuel which is not adapted to steady idling of the engine, the position of port 182 may be changed to the dotted position of 182A above the position 182 such that the conduit 181 no longer is in communication with the intake manifold when the throttle valve is closed. Therefore, in the idle condition of the engine, piston 25 is subjected only to atmospheric pressure and spring 118 draws the piston down such that stem 112 contacts the valving member 72 to open the port 158 (see FIG. 5) connecting to the high octane supply chamber 32. The engine thus is supplied through chamber 149 and the idler tube 169 with the fuel proper for idling. No fuel flows from the high octane bowl to the venturi tube since the throttle valve is closed across the throttle chamber.

FIG. 7 illustrates the arcuate displacement of the vertical runs of the conduit 181 and passage 191 with respect to the venturi tube in the fuel intake. This physical arrangement is onlyone of many contemplated by the invention and may vary with the size and general arrangement of the particular carburetor of the invention. Obviously the invention is not restricted to the single throat carburetors which are illustrative in this disclosure, but may be used with equal facility with carburetors of dual or multiple throats by mechanical arrangements common to this field of art.

Field tests of carburetors in accordance with the invention have demonstrated substantial reduction in polluting emissions when compared to conventional carburetors. Such tests also showed that a substantial proportion of harmful emissions is engendered with conventional carburetors during deceleration when the idle valve supplies unneeded gasoline to an engine havin g no fuel requirements for power. It is therefore desirable to have a carburetor which controls the fuel supply to the engine during periods of deceleration without interfering with normal idling operation. FIG. 8 illustrates such an embodiment of the invention. The carburetor 200 of FIG. 8 is substantially similar to the embodiment of FIG. 6, having no elongate tubes connecting between the throttle chamber and the piston cylinder 24. The embodiment of FIG. 8 has a conduit 18] which, depending upon the idle fuel desired, has an entry port 182 or 182A opening on one or the other side of the closed position of the throttle valve 46. Both ports may be supplied on manufacture and one plugged as desired. In the embodiment of FIG. 6 fuel is drawn over from a fuel chamber 149 by a conventional idler tube 169 when the throttle closes. In the embodiment of FIG. 8, the cylinder 24 of the control piston 25 has a bottom plug 201 which not only journals stem 112 but is ported to break the idle valve suction on the idler tube when the piston 25 is raised by the manifold vacuum to the top ofthe cylinder. Stem 112 has an annular groove 203 which registers under certain conditions with a transverse passage 205 through the plug. The passage connects to an annular groove 206 in the plug periphery which, in turn, connects to an L-shaped passage 207 in upper casting 12 which communicates with an air passage 208 through the top of the idler tube. This passage can be easily added to the conventional idler tube.

An air passage 208 extends horizontally from the threaded bore into which the plug seats. A connecting vertical passage 211 communicates with the area above the fuel level 212 within float chamber 32.

The air above the fuel level in both float bowls is replenished through a conventional air bleeder cap 214 which may enter into either bowl but is shown connected to bowl 31 in FIG. 8. The wall 53 between bowls has an upper bleeder hole 216 such that the air pressure above the fuel level is the same in both the float bowls.

In operation, the embodiment of FIG. 8 is similar in most conditions of operation to the embodiment of FIG. 6. However, under deceleration, when the piston 25 is raised in the cylinder 24 against a calibrating spring 215, the idler passage 19] draws air through the cylinder plug 201 from the-area above the fuel level instead of drawing fuel from chamber 149 to the idle valve. Spring 215 is chosen to oppose rise of piston 25 above the dotted position 25A so as to differentiate between sensing normal idling conditions and deceleration conditions of manifold vacuum level. Thus unusable fuel is not delivered to the engine and expelled to the atmosphere as unburned hydrocarbons.

Several modifications of the invention have been shown in the illustrative embodiments. However, the embodiments are to be regarded as illustrative only since, for simplicity, they show only schematic singlebarrel carburetors, whereas the invention is applicable to carburetors of multiple barrels, as well. Many variations within the scope of the invention, other than those suggested in the above disclosure, will occur to those skilled in this particular art. It is therefore desired that the scope of the invention be measured by the appended claims, rather than the illustrative disclosure made herein.

I claim:

1. In an internal combustion engine for use with two fuel supplies and having fuel intake means-with a throttle valve therein, the combination comprising a first fuel bowl connecting to the first fuel supply, a second fuel bowl connecting to the second fuel supply, a fuel chamber affording passage to the fuel intake means from the fuel bowls, a single valving member intervening between both fuel bowls and the fuel chamber, a spring biasing the valving member, control means responsive to engine manifold vacuum conditions for displacing the valving member between mutually exclusive open positions with respect to each fuel bowl; said control means having a piston chamber, a piston in the chamber, a conduit connecting between the intake means adjacent the manifold and the piston chamber and piston, a spring opposing piston response to increased manifold vacuum, a contact element on the piston adapted to change the condition of the valving member, and a shut-off valve in the conduit remote from the fuel intake means; an idle passage from the fuel chamber to thelfuel intake means, and means for metering the fuel flow between the valving member and the fuel chamber.

2. Apparatus in accordance with claim 1 wherein the valving member comprises a valve chamber a first port opening to the first fuel bowl, a second port opening to the second fuel bowl, a valve plunger having valving elements at each end operatively responsive to the control means responsive to manifold vacuum conditions to alternatively open and close the first and second ports substantially simultaneously, said valving member spring biasing the valve plunger in opposition to the low vacuum condition of the means responsive to manifold vacuum conditions; said apparatus further comprising an idle passage between the valve chamber and the engine fuel intake means. 

1. In an internal combustion engine for use with two fuel supplies and having fuel intake means with a throttle valve therein, the combination comprising a first fuel bowl connecting to the first fuel supply, a second fuel bowl connecting to the second fuel supply, a fuel chamber affording passage to the fuel intake means from the fuel bowls, a single valving member intervening between both fuel bowls and the fuel chamber, a spring biasing the valving member, control means responsive to engine manifold vacuum conditions for displacing the valving member between mutually exclusive open positions with respect to each fuel bowl; said control means having a piston chamber, a piston in the chamber, a conduit connecting between the intake means adjacent the manifold and the piston chamber and piston, a spring opposing piston response to increased manifold vacuum, a contact element on the piston adapted to change the condition of the valving member, and a shut-off valve in the conduit remote from the fuel intake means; an idle passage from the fuel chamber to the fuel intake means, and means for metering the fuel flow between the valving member and the fuel chamber.
 2. Apparatus in accordance with claim 1 wherein the valving member comprises a valve chamber a first port opening to the first fuel bowl, a second port opening to the second fuel bowl, a valve plunger having valving elements at each end operatively responsive to the control means responsive to manifold vacuum conditions to alternatively open and close the first and second ports substantially simultaneously, said valving member spring biasing the valve plunger in opposition to the low vacuum condition of the means responsive to manifold vacuum conditions; said apparatus further comprising an idle passage between the valve chamber and the engine fuel intake means. 